Serial Grinding Research Articles

A Novel Technique for Producing Three-Dimensional Data Using Serial Sectioning and Semi-Automatic Image Classification.

The three-dimensional characterization of internal features, via metrics such as orientation, porosity, and connectivity, is important to a wide variety of scientific questions. Many spatial and morphological metrics only can be measured accurately through direct in situ three-dimensional observations of large (i.e., big enough to be statistically representative) volumes. For samples that lack material contrast between phases, serial grinding and imaging—which relies solely on color and textural characteristics to differentiate features—is a viable option for extracting such information. Here, we present the Grinding, Imaging, Reconstruction Instrument (GIRI), which automatically serially grinds and photographs centimeter-scale samples at micron resolution. Although the technique is destructive, GIRI produces an archival digital image stack. This digital image stack is run through a supervised machine-learning-based image processing technique that quickly and accurately segments data into predefined classes. These classified data then can be loaded into three-dimensional visualization software for measurement. We share three case studies to illustrate how GIRI can address questions with a significant morphological component for which two-dimensional or small-volume three-dimensional measurements are inadequate. The analyzed metrics include: the morphologies of objects and pores in a granular material, the bulk mineralogy of polyminerallic solids, and measurements of the internal angles and symmetry of crystals.

Restudy of string fossils from the Ediacaran-Cambrian Liuchapo Formation in Guizhou Province, South China

String fossils, Horodyskia and Palaeopascichnus are globally distributed in Proterozoic strata. They are composed of uniform segments with specific intervals, and their origins have been debated for decades. Horodyskia consists of spherical or subspheroidal segments, and has been interpreted as eukaryote, seaweeds, foraminifera, and pseudofossils; Palaeopascichnus is composed of crescent or sausage-shaped segments and has been interpreted as trace fossils or protozoans. A large number of string fossils are found from the Liuchapo Formation in South China, which are similar to Horodyskia minor and Palaeopascichnus jiumenensis. However, the classification of H. minor and P. jiumenensis remains debatable because of their small size, inter-segment connection, and the external quartz halo. In order to further explore the biological attributes and affinities of these two string fossils, we studied the chert samples of the Liuchapo Formation from Jiumen, Jinlongcun and Bahuang sections in Guizhou Province, and reconstructed the morphological characteristics of the string fossils using the methods of thin section observation and serial grinding. Based on the reconstruction, we renamed the string fossils and erected two new genera, Parahorodyskia and Ordinilunulatus. Parahorodyskia consists of even-sized spherical and ellipsoidal segments with consistent spacing, surrounded by a peapod-shaped halo. According to the absence or presence of the ribbon-like connection, two species are identified: P. disjuncta, and P. minor. Ordinilunulatus consists of uniform, evenly spaced disk-shaped segments with a terminal spherical structure, surrounded by a sausage-shaped halo, and segments are generally jointed by connection. On the basis of three-dimensional reconstruction, string fossils Parahorodyskia and Ordinilunulatus of the Liuchapo Formation are more likely to be of biological rather than diagenetic origin. In addition, a strip-like fossil is also discovered in abundance in the Liuchapo Formation. This strip-like fossil is described as a new erected genus Jiumenia, and it shares similar outer halo structure with the Liuchapo string fossils. Both Parahorodyskia and Ordinilunulatus might be affiliated to protist. Finally, the wide occurrences of Parahorodyskia and Ordinilunulatus in South China may imply their potential biostratigraphic significance for the bedded cherts in the Ediacaran-Cambrian transition.

Three‐Dimensional Morphometry of Ooids in Oolites: A New Tool for More Accurate and Precise Paleoenvironmental Interpretation

AbstractThe prevalence of ooids in the stratigraphic record, and their association with shallow‐water carbonate environments, make ooids an important paleoenvironmental indicator. Recent advances in the theoretical understanding of ooid morphology, along with empirical studies from Turks and Caicos, Great Salt Lake, and The Bahamas, have demonstrated that the morphology of ooids is indicative of depositional environment and hydraulic conditions. To apply this knowledge from modern environments to the stratigraphic record of Earth’s history, researchers measure the size and shape of lithified ooids on two‐dimensional surfaces (i.e., thin sections), often assuming that random 2D slices intersect the nuclei and that the orientation of the ooids is known. Here, we demonstrate that these assumptions rarely are true, resulting in errors of up to 35% for metrics like major axis length. We present a method for making 3D reconstructions by serial grinding and imaging, which enables accurate measurement of the morphology of individual ooids within an oolite, as well as the sorting and porosity of a sample. We also provide three case studies that use the morphology of ooids in oolites to extract environmental information. Each case study demonstrates that 2D measurements can be useful if the environmental signal is large relative to the error from 2D measurements. However, 3D measurements substantially improve the accuracy and precision of environmental interpretations. This study focuses on oolites, but errors from 2D measurements are not unique to oolites; this method can be used to extract accurate grain and porosity measurements from any coherent, granular sample.

Simulation of axicon processing area on technological equipment

Annotation. An analytical expression is obtained for engineering calculation of the regularities of removing the allowance from the flat surface of the part (a rectangle in the form of a flat glass plate of considerable thickness with holes for axicon blanks), which participates in relative and portable movement on the surface of a rotating tool (faceplate) and is in a power circuit with it, which provides automatic self-installation of lapping surfaces. A scheme is proposed for dividing the lapping surfaces of a flat tool and part into ring zones and sectors, resulting in the formation of elementary platforms with reference (calculated) points in their center. Analytical expressions are obtained for calculating the coordinates of these points. The kinematics of the relative movement of the tool and the straightener without oscillation of the upper link is considered, while the sliding of the conjugate surfaces takes place due to rotation of the tool and the straightener installed with a certain eccentricity. An expression is obtained for determining the sliding speed at any point of contact of the conjugate surfaces. Modeling when dealing with relative and portable movement of the upper unit, which allowed obtaining a formula for the slip velocity of the straightener relative to the tool that allows calculation the path of friction in a particular zone in different modes of operation of technological equipment. Modeling can be used as the basis for creating a method for controlling the process of forming conical optical parts (axicons) on serial lever grinding and polishing machines with a flat tool under free lapping conditions, which provide the possibility of obtaining axicons with a deviation of the forming cone from the straightness of no more than ±0.00012 mm.

The Herefordshire Lagerstätte: fleshing out Silurian marine life

The Herefordshire Lagerstätte ( c . 430 Ma) from the UK is a rare example of soft-tissue preservation in the Silurian. It yields a wide range of invertebrates in unparalleled three-dimensional detail, dominated by arthropods and sponges. The fossils are exceptionally preserved as calcitic void infills in early diagenetic carbonate concretions within a volcaniclastic (bentonite) horizon. The Lagerstätte occurs in an outer shelf/upper slope setting in the Welsh Basin, which was located on Avalonia in the southern subtropics. The specimens are investigated by serial grinding, digital photography and rendering in the round as ‘virtual fossils’ by computer. The fossils contribute much to our understanding of the palaeobiology and early history of the groups represented. They are important in demonstrating unusual character combinations that illuminate relationships; in calibrating molecular clocks; in variously linking with taxa in both earlier and later Paleozoic Lagerstätten; and in providing evidence of the early evolution of crown-group representatives of several groups.

Multiscale approach reveals that Cloudina aggregates are detritus and not in situ reef constructions

The earliest metazoans capable of biomineralization appeared during the late Ediacaran Period (635-541 Ma) in strata associated with shallow water microbial reefs. It has been suggested that some Ediacaran microbial reefs were dominated (and possibly built) by an abundant and globally distributed tubular organism known as Cloudina If true, this interpretation implies that metazoan framework reef building-a complex behavior that is responsible for some of the largest bioconstructions and most diverse environments in modern oceans-emerged much earlier than previously thought. Here, we present 3D reconstructions of Cloudina populations, produced using an automated serial grinding and imaging system coupled with a recently developed neural network image classifier. Our reconstructions show that Cloudina aggregates are composed of transported remains while detailed field observations demonstrate that the studied reef outcrops contain only detrital Cloudina buildups, suggesting that Cloudina played a minor role in Ediacaran reef systems. These techniques have wide applicability to problems that require 3D reconstructions where physical separation is impossible and a lack of density contrast precludes tomographic imaging techniques.

Three-Dimensional Morphology of Beaconites capronus from Northeast England

ABSTRACTBeaconites capronus is a winding meniscate backfilled trace fossil differentiated from comparable ichnotaxa Taenidium and Ancorichnus on the basis of its distinct and unornamented burrow lining. Typically, horizontal to subhorizontal B. capronus also includes vertical pipes, which serve as a point of entry for endobenthic deposit feeding activity. The burrows do not self-cross but often display secondary successive branching potentially indicating coprophagous feeding strategies in lower nutrient sediment. Beaconites capronus material is examined and discussed from the Carboniferous offshore transition zone deposits near Howick, United Kingdom. Samples were collected and analyzed using high-resolution serial grinding and modeling techniques documenting fine detail in three dimensions. As the burrows are actively backfilled and do not maintain a connection to the sediment water interface the trace making organism must have a method of coping with the low oxygen porewater conditions. Four methods are considered herein, as follows: 1) revisiting the sediment-water interface; 2) creating periodic shafts; or 3) employing the use of obligate anaerobic metabolism. Based on the material presented herein, an emended ichnospecific diagnosis is provided.

Three-Dimensional Morphological and Permeability Modelling of Diplocraterion

ABSTRACTThree-dimensional mini-permeametry of Diplocraterion burrows from the Middle Jurassic Scarborough Formation of North Yorkshire, UK, reveals some of the relationships between ichnofossils and reservoir quality in conventional siliciclastic petroleum reservoir facies. This work focuses on the effect that the various Diplocraterion burrowing behaviours have on the permeability characteristics of the near-burrow environment. Samples were studied using serial grinding and mini-permeametry. This is the first documented attempt at combining these techniques to create an integrated understanding of the inter relationship of trace fossil morphology and reservoir quality in three dimensions. Palaeobiological insights arising from the three-dimensional modelling include evidence for resuspension feeding, deposit feeding, sediment cleaning and “collapse-cone feeding.” Higher than expected permeability values (>150 mD) were measured from the sandy shafts of Diplocraterion and adjacent areas. Zones of enhanced permeability associated with the inter-shaft area are inferred to result from sediment cleaning, and grain-size selective deposit feeding. Bioturbation by Diplocraterion is found to improve reservoir quality by sediment cleaning and creation of highly permeable vertical conduits in a reservoir facies with otherwise low permeability.

VIRTUAL PALEONTOLOGY—AN OVERVIEW

AbstractVirtual paleontology is the study of fossils through three-dimensional digital visualizations; it represents a powerful and well-established set of tools for the analysis and dissemination of fossil data. Techniques are divisible into tomographic (i.e., slice-based) and surface-based types. Tomography has a long predigital history, but the recent explosion of virtual paleontology has resulted primarily from developments in X-ray computed tomography (CT), and of surface-based technologies (e.g., laser scanning). Destructive tomographic methods include forms of physical-optical tomography (e.g., serial grinding); these are powerful but problematic techniques. Focused Ion Beam (FIB) tomography is a modern alternative for microfossils; it is also destructive but is capable of extremely high resolutions. Nondestructive tomographic methods include the many forms of CT, which are the most widely used data-capture techniques at present, but are not universally applicable. Where CT is inappropriate, other nondestructive technologies (e.g., neutron tomography, magnetic resonance imaging, optical tomography) can prove suitable. Surface-based methods provide portable and convenient data capture for surface topography and texture, and might be appropriate when internal morphology is not of interest; technologies include laser scanning, photogrammetry, and mechanical digitization. Reconstruction methods that produce visualizations from raw data are many and various; selection of an appropriate workflow will depend on many factors, but is an important consideration that should be addressed prior to any study. The vast majority of three-dimensional fossils can now be studied using some form of virtual paleontology, and barriers to broader adaptation are being eroded. Technical issues regarding data sharing remain problematic. Technological developments continue; those promising tomographic recovery of compositional data are of particular relevance to paleontology.

Three-dimensional morphology and palaeobiology of the trace fossil Dactyloidites jordii nov. isp. from the Carboniferous of England

The diverse ichnological assemblage from the outcrops near Howick (Northumberland, United Kingdom) is exceptionally well-preserved. Among these Carboniferous ichnotaxa is a new ichnospecies of Dactyloidites. Specimens were collected and processed using high-resolution serial grinding and photography to produce an accurate and precise three-dimensional model of these new burrows in full colour. The model produced in association with petrographic thin sections and field observations is used as the basis for comparison between Dactyloidites jordii nov. isp. and other ichnospecies of Dactyloidites. The current taxonomic status of the ichnogenus is examined and reviewed. D. jordii nov. isp. is a broadly bisymmetrical, stellate to palmate burrow composed of numerous long, narrow rays that exhibit three orders of branching arranged into tiered galleries radiating from a central shaft. The trace maker is suggested to be a vermiform organism with an adaptive burrowing strategy that facilitates alteration of its burrow construction to accommodate suboptimal sediment conditions. The adaptive nature of trace-making organisms and the inherent anisotropy of many burrowed media highlight the need for ichnologists to provide a type series rather than a single holotype, in order to capture the inherent range of common burrow morphologies.

Ichnology and palaeobiology of Phoebichnus trochoides from the Middle Jurassic of north‐east England

AbstractPhoebichnus trochoides is a large, radiating trace fossil most commonly found in shallow marine siliciclastic deposits. The structure consists of a central boss from which extend numerous, lined, radiating burrows which have an active fill. Serial grinding and modelling techniques allow the full three‐dimensional morphology of Phoebichnus trochoides to be constructed for the first time. Three‐dimensional models of the trace fossil demonstrate that the central zone is composed of stacked disc‐shaped layers. The structure is inferred to result from collapse of sediment below a surficial cone created by the trace‐maker from excavated sediment produced during burrowing. The fill of the radial burrows is herein determined to be composed of angle of repose laminae that are inclined towards the central zone rather than the meniscate backfill documented in the ichnogeneric diagnosis and all subsequent descriptions. The structure of the fill resulted from the trace‐making organism filling its burrows from a dwelling position close to the central boss, probably with material excavated from other parts of the burrow system. This study also reports for the first time subtle conical structures above the radial galleries that are inferred to result from collapse cone feeding. The new fully three‐dimensional data set created of the burrow and the near‐burrow environment allows for a new palaeobiological understanding of the burrow, which suggests that a crustacean trace‐maker is most likely.

The dynamic influence of microbial mats on sediments: fluid escape and pseudofossil formation in the Ediacaran Longmyndian Supergroup, UK

Microbial mats are thought to have been widespread in marine settings before the advent of bioturbation, and the range of their influence on sediments is gradually becoming recognized. We propose that mat sealing can dynamically affect porewater conditions, and allow the build-up of overpressure that can drive dewatering and degassing to produce a suite of atypical fluid-escape features. Finely bedded silty and sandy laminae from the c . 560 Ma Burway Formation of the Longmyndian Supergroup, Shropshire, England, reveal evidence for sediment injection, including disrupted bedding, clastic injections, sill-like features and sediment volcanoes at sub-millimetre scale. These features are associated with crinkly laminae diagnostic of microbial matgrounds. Matground-associated sediment injection can explain the formation of several types of enigmatic discoidal impressions, common in rocks of this age, which have previously been attributed to the Ediacaran macrobiota. Serial grinding of Longmyndian forms previously described as Medusinites aff. asteroides and Beltanelliformis demonstrates that such discoidal features can be fully explained by fluid escape and associated load structures. Our observations emphasize the non-actualistic nature of shallow-marine Ediacaran sediments. Matground-associated sediment injection features provide a new insight into the interpretation of Proterozoic rocks and the biogenicity of their enigmatic discoidal markings. Supplementary materials: A document containing further images of fluid escape and loading features observed in the upper Burway Formation at Ashes Hollow, together with an annotated diagram of features appearing in one typical vertical cross-section, is available at www.geolsoc.org.uk/SUP18870 .

Reconstructing the Auditory Apparatus of Therapsids by Means of Neutron Tomography

The internal cranial structure of mammalian ancestors, i.e. the therapsids or “mammal-like reptiles”, is crucial for understanding the early mammalian evolution. In the past therapsid skulls were investigated by mechanical sectioning or serial grinding, which was a very time-consuming and destructive process and could only be applied to non-valuable or poorly preserved specimens. As most therapsid skulls are embedded in terrestrial iron-rich sediments of Late Permian or Triassic age, i.e. so called “Red beds”, a successful investigation with X-Rays is often not possible.We successfully investigated therapsid skulls by means of neutron tomography at the facility ANTARES at FRM II in Munich using cold neutron radiation. This kind of radiation is able to penetrate iron-rich substances in the range between 5 and 15cm and produces a good contrast between matrix and bones, which enables segmentation of internal cranial structures such as bones, cavities and canals of nerves and blood vessels. In particular, neutron tomography combined with methods of 3D modeling was used here for the investigation and reconstruction of the auditory apparatus of therapsids.

Growth trajectories of some major ammonoid sub-clades revealed by serial grinding tomography data

Molluscs such as ammonoids record their growth in their accretionary shells, making them ideal for the study of evolutionary changes in ontogeny through time. Standard methods usually focus on two-dimensional data and do not quantify empirical changes in shell and chamber volumes through ontogeny, which can possibly be important to disentangle phylogeny, interspecific variation and palaeobiology of these extinct cephalopods. Tomographic and computational methods offer the opportunity to empirically study volumetric changes in shell and chamber volumes through ontogeny of major ammonoid sub-clades in three dimensions (3-D). Here, we document (1) the growth of chamber and septal volumes through ontogeny and (2) differences in ontogenetic changes between species from each of three major sub-clades of Palaeozoic ammonoids throughout their early phylogeny. The data used are three-dimensional reconstructions of specimens that have been subjected to grinding tomography. The following species were studied: the agoniatitid Fidelites clariondi and anarcestid Diallagites lenticulifer (Middle Devonian) and the Early Carboniferous goniatitid Goniatites multiliratus. Chamber and septum volumes were plotted against the septum number and the shell diameter (proxies for growth) in the three species; although differences are small, the trajectories are more similar among the most derived Diallagites and Goniatites compared with the more widely umbilicate Fidelites. Our comparisons show a good correlation between the 3-D and the 2-D measurements. In all three species, both volumes follow exponential trends with deviations in very early ontogeny (resolution artefacts) and near maturity (mature modifications in shell growth). Additionally, we analyse the intraspecific differences in the volume data between two specimens of Normannites (Middle Jurassic).

First report of fossil "keratose" demosponges in Phanerozoic carbonates: preservation and 3-D reconstruction.

Fossil record of Phanerozoic non-spicular sponges, beside of being important with respect to the lineage evolution per se, could provide valuable references for the investigation of Precambrian ancestral animal fossils. However, although modern phylogenomic studies resolve non-spicular demosponges as the sister group of the remaining spiculate demosponges, the fossil record of the former is extremely sparse or unexplored compared to that of the latter; the Middle Cambrian Vauxiidae Walcott 1920, is the only confirmed fossil taxon of non-spicular demosponges. Here, we describe carbonate materials from Devonian (Upper Givetian to Lower Frasnian) bioherms of northern France and Triassic (Anisian) microbialites of Poland that most likely represent fossil remnants of keratose demosponges. These putative fossils of keratose demosponges are preserved as automicritic clumps. They are morphologically distinguishable from microbial fabrics but similar to other spiculate sponge fossils, except that the skeletal elements consist of fibrous networks instead of assembled spicules. Consistent with the immunological behavior of sponges, these fibrous skeletons often form a rim at the edge of the automicritic aggregate, separating the inner part of the aggregate from foreign objects. To confirm the architecture of these fibrous networks, two fossil specimens and a modern thorectid sponge for comparison were processed for three-dimensional (3-D) reconstruction using serial grinding tomography. The resulting fossil reconstructions are three-dimensionally anastomosing, like modern keratose demosponges, but their irregular and nonhierarchical meshes indicate a likely verongid affinity, although a precise taxonomic conclusion cannot be made based on the skeletal architecture alone. This study is a preliminary effort, but an important start to identify fossil non-spicular demosponges in carbonates and to re-evaluate their fossilization potential.

Three-dimensional histological specimen preparation for accurate imaging and spatial reconstruction of the middle and inner ear

Purpose This paper presents a highly accurate cross-sectional preparation technique. The research aim was to develop an adequate imaging modality for both soft and bony tissue structures featuring high contrast and high resolution. Therefore, the advancement of an already existing microgrinding procedure was pursued. The central objectives were to preserve spatial relations and to ensure the accurate three-dimensional reconstruction of histological sections.Methods Twelve human temporal bone specimens including middle and inner ear structures were utilized. They were embedded in epoxy resin, then dissected by serial grinding and finally digitalized. The actual abrasion of each grinding slice was measured using a tactile length gauge with an accuracy of one micrometre. The cross-sectional images were aligned with the aid of artificial markers and by applying a feature-based, custom-made auto-registration algorithm. To determine the accuracy of the overall reconstruction procedure, a well-known reference object was used for comparison. To ensure the compatibility of the histological data with conventional clinical image data, the image stacks were finally converted into the DICOM standard.Results The image fusion of data from temporal bone specimens’ and from non-destructive flat-panel-based volume computed tomography confirmed the spatial accuracy achieved by the procedure, as did the evaluation using the reference object.Conclusion This systematic and easy-to-follow preparation technique enables the three-dimensional (3D) histological reconstruction of complex soft and bony tissue structures. It facilitates the creation of detailed and spatially correct 3D anatomical models. Such models are of great benefit for image-based segmentation and planning in the field of computer-assisted surgery as well as in finite element analysis. In the context of human inner ear surgery, three-dimensional histology will improve the experimental evaluation and determination of intra-cochlear trauma after the insertion of an electrode array of a cochlear implant system.

The Recognition of Ophiomorpha irregulaire on the Basis of Pellet Morphology: Restudy of Material from the Type Locality

Serial grinding of a specimen of Ophiomorpha irregulaire collected from Coal Creek Canyon in the Book Cliffs of Utah, USA—the type locality of the ichnospecies—allows us to assess the validity of pellet morphology as an ichnotaxobase for species-level identification. The importance of O. irregulaire stems from its abundance in petroliferous shallow marine strata of post-Paleozoic age. Our three-dimensional reconstruction of the burrow wall of O. irregulaire demonstrates for the first time that it is composed of sand-cored pellets. The typically spiky nature of the pellets in cross-section is inferred to result from differential compaction of the sand core and pelletal lining. Rupturing of the thin outer clay coating of the sand pellets is considered to produce the distinctively attenuated, spiky outer surface to the burrow wall of this ichnospecies. This study demonstrates the utility of pellet morphology in species-level classification of Ophiomorpha and lends support to O. irregulaire being a cosmopolitan ichnospecies present in post-Paleozoic strata. It also demonstrates the need to ensure that ichnotaxonomic identifications are based on three-dimensional knowledge of the trace fossil in question.

Fossilized digestive systems in 23 million-year-old wood-boring bivalves

Fossilized remnants of parts of the digestive system of wood-boring pholadoidean bivalves are reported from late Oligocene –early Miocene deep-water sediments in western Washington State, USA. They are reconstructed using serial grinding tomography and computer-based 3D visualizations. Two types are distinguished: (1) a U-shaped structure with a groove on its inner side, interpreted as the caecum of xylophagaines; (2) an elongate structure with a central groove and thin tubes running parallel to it on its dorsal and ventral side, interpreted as the caecum and the intestine, respectively, of teredinids. Petrological thin-section observations show that these structures are filled by a mass of fine woody material, suggesting that being filled with woody material facilitated their fossilization. Screening the fossil record for similar structures in Mesozoic pholadoidean fossils can potentially help to clarify feeding strategies, phylogenetic relationships and the evolution of feeding strategies among early pholadoidean bivalves.

3D morphometry of polyconitid rudist bivalves based on grinding tomography

Previous taxonomic studies have shown that polyconitid rudists have a characteristic arrangement of the myocardinal system with an ectomyophoral cavity on the posterior side of the left valve. The specific arrangement of the myophores and associated cavities defines the different genera. However, there has been little research on the three-dimensional spatial distribution and size of the internal features, for want of a technique that is suitable for large and low density-contrast specimens. The tomographic technique described herein is based on automatic serial grinding and serial scanning; the resulting images are treated with biomedical image software. The technique has been applied to a pair of well-preserved specimens of Polyconites verneuili from the Upper Aptian of Spain. Fifteen quantitative characters have been obtained using multiplanar virtual cuts, volume-rendering, and isosurfaces reconstructions. The study revealed the shape, size, and distribution of the ectomyophoral, body and accessory cavities, the lengths and volumes of the teeth, and the arrangement of the myophores. We conclude that this technique facilitates the description of rudist bivalves and is suitable for other fossils; moreover, it has the potential to be used in other fields of geology.

Bone vascularization and growth in placoderms (Vertebrata): The example of the premedian plate of Romundina stellina Ørvig, 1975

The Placodermi (armored jawed fishes), which appeared during the Lower Silurian and disappeared without leading any descendants at the end of the Famennian (Latest Devonian), have the highest diversity of known Devonian vertebrate groups. As phylogenetically basal gnathostomes (jawed vertebrates), they are potentially informative about primitive jawed vertebrate anatomy and origins. Until recently, the study of their internal or histological structures has required destructive methods such as sectioning or serial grinding. Recent advances in tomography and imaging technologies, especially through the increasing use of synchrotron phase contrast imaging for the study of fossils, allow us to reveal the inner structures of the fossil nondestructively and with unprecedented three-dimensional level of detail. Here, we present for the first time the prerostral anatomy of the small acanthothoracid Romundina stellina, one of the earliest and most basal placoderms. Phase contrast imaging allows us to reconstruct the vascularization and nerve canals of the premedian plate and adjacent parts of the skeleton three-dimensionally in great detail, providing important clues to the growth modes and biology of the animal.